Chapter 13 : Synthetic Fibers and Plastics
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1. ________ and ________ are examples of natural
fibres.
ANS: cotton and wool
2. The simplest molecule of a polymer is known as a
________.
ANS: monomer
3. Rayon is also known as a ________ fibre.
ANS: regenerated
4. Nylon is a ________ fibre.
ANS: synthetic
5. ________ plastics cannot be remoulded again on
heating.
ANS: thermosetting
1. Natural fibres are highly resistant to the effects
of chemicals like acids and alkalis.
ANS: False
2. Synthetic fibres absorb very little water.
ANS: True
3. Thermoplastics can be easily remoulded on heating.
ANS: True
4. The plastic, used for insulating electrical wires,
is teflon.
ANS: True
5. All types of plastics are biodegradable.
ANS: False
1. The correct choice, for the box, in the following
sequence, is—
thermoplastic : PVC ; thermosetting plastic : ?
•
nylon
•
polystyrene
•
bakelite
•
polythene
ANS: bakelite
2. Which of the following is also known as the ‘wonder polymer’?
•
nylon
•
polystyrene
•
polythene
•
acrylic
ANS: nylon
3. A highly durable synthetic fibre, used for making
parachutes and ropes for rock climbing and fishing nets, is—
•
rayon
•
nylon
•
terylene
•
PET
ANS: nylon
4. Which of the following is NOT one of the
characteristics of synthetic fibres?
•
easy to clean
and dry quickly.
•
long lasting
lustre.
•
biodegradable.
•
do not shrink
on washing.
ANS:
biodegradable
5. Melamine is a thermosetting plastic; for it one can
say that—
•
it can be
easily remoulded on heating.
•
it cannot
resist fire.
•
it has a
cross-linked arrangement of molecules.
•
its ‘tolerance’,
towards heat is very much lower than those of other plastics.
ANS: it has a cross-linked arrangement of molecules.
6. Which of the following is a correct statement about
synthetic plastics?
•
thermoplastics
cannot be deformed easily on heating.
•
synthetic
plastics are biodegradable.
•
synthetic
plastics get easily affected by acids and alkalis.
•
synthetic
plastics have quite high tensile strengths.
ANS: synthetic plastics have quite high tensile
strengths.
1. Define the term ‘synthetic fibres’.
ANS: Synthetic fibres are man-made fibres prepared by
chemical processing of small units called monomers. These are artificial fibres
made by joining many simple molecules to form polymers.
2. Write two uses of rayon.
ANS:
A. Rayon is used for making clothes
such as sarees and dresses.
B. Rayon is used in industries for
making tyre cords and surgical products.
3. Name two other articles that can be made from
nylon.
ANS: Two other articles made from nylon are ropes and
seat belts.
4. Why are clothes made from synthetic fibres
uncomfortable in summer?
ANS: Clothes made from synthetic fibres are
uncomfortable in summer because they absorb very little sweat and do not allow
proper evaporation, making the body feel hot and sticky.
5. Give two examples each of thermoplastics and
thermosetting plastics.
ANS:
Thermoplastics: Polythene, PVC
Thermosetting plastics: Bakelite, Melamine
1. How is a ‘regenerated
fibre’
different from a true synthetic
fibre? Give one example of each of these types of fibres.
ANS: A regenerated fibre is made by chemically
processing a natural fibre, whereas a true synthetic fibre is made entirely by
chemical synthesis without using any natural fibre.
Example of regenerated fibre: Rayon
Example of true synthetic fibre: Nylon
2. Why do clothes made of nylon last longer?
ANS: Clothes made of nylon last longer because nylon
is strong, elastic, durable, wrinkle-resistant and does not wear out easily.
3. Write two points of differences between
thermosetting plastics and thermoplastics.
ANS:
Thermoplastics
They have a linear arrangement of molecules.
They soften on heating and can be remoulded.
Thermosetting plastics
They have a cross-linked arrangement of molecules.
They do not soften on heating and cannot be remoulded.
4. State any three advantages of synthetic fibres.
ANS:
A. Synthetic fibres are strong and
durable.
B. They dry quickly.
C. They are wrinkle-resistant and easy
to maintain.
5. Give your views on the following: ‘Excessive use of plastics is a
threat to environment.’
ANS: Excessive use of plastics is a threat to the
environment because plastics are non-biodegradable and take many years to
decompose. They pollute soil and water, clog drains, harm animals when
swallowed and release poisonous gases when burnt. Therefore, plastic use should
be reduced and managed carefully.
6. Why is bakelite a good choice for making electrical
switches and handles of cooking utensils?
ANS: Bakelite is a good choice for making electrical
switches and handles of cooking utensils because it is a poor conductor of heat
and electricity and can withstand high temperature without melting.
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